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Ch. 7: Peridot

Ch. 7: Garnet Page of 149 Ch. 7: Peridot Text size:minus plus Restore normal size   Mail page  Print this page
       
     
 
PERIDOT.
85
  
 
 
  
 
black garnets used in the 18th century in mourning jewellery ; of the yellow and greenish-yellow garnets known as topazolite, and of colophonite which resembles common rosin : all these are essen­tially calcium ferric garnet, and with demantoid are included under andradite.
Peridot.
Under the species olivine are now included both the yellow and greenish-yellow chrysolite and the pistachio green or leek green peridot, or evening emerald. The latter possesses a quieter hue than the emerald, and needs to be in rather large pieces that its colour may be properly developed. Perhaps the peculiar hue of the peridot may be best suggested by that seen on looking through a delicate green leaf. It contains more yellow and grey than the emerald. The peridot is dichroic, giving a straw yellow and a green image.* It crystallizes in the orthorhorrîbic system. Its hardness is unfortunately rather low, about 6'5, so that polished specimens are easily scratched by wear. The peridot is, however, well suited for engraving, and forms, when set in black and white, or orange enamel and gold, a beautiful stone for pendants. En­graved peridots are, however, with very few exceptions, of modern date. The specific gravity of the peridot is not changed by heat. A careful determination of the specific gravity of a fine rich-coloured peridot gave 3'389. A range of 3-35 to 3'44 is usually assigned to this variety of the "precious olivine."
Fine peridots come from Egypt, but most of the large specimens now met with are derived from old ecclesiastical and other orna­ments. But during recent years at least one Egyptian locality has been discovered or re-discovered. One of the peculiarities of olivine is its occurrence in meteorites. There are some good peridots in the Townshend collection, and characteristic specimens in the British Museum and in the Museum of Practical Geology.
* Fig. 4. Frontispiece.
  
 
 
  
       
Ch. 7: Garnet Page of 149 Ch. 7: Peridot
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